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Metasurfaces are arrays of subwavelength spaced nanostructures that can manipulate the amplitude, phase, and polarization of light to achieve a variety of optical functions beyond the capabilities of 3D bulk optics. However, they suffer from limited performance and efficiency when multiple functions with large deflection angles are required because the non-local interactions due to optical coupling between nanostructures are not fully considered. Here we introduce a method based on supercell metasurfaces to demonstrate multiple independent optical functions at arbitrary large deflection angles with high efficiency. In one implementation the incident laser is simultaneously diffracted into Gaussian, helical and Bessel beams over a large angular range. We then demonstrate a compact wavelength-tunable external cavity laser with arbitrary beam control capabilities – including beam shaping operations and the generation of freeform holograms. Our approach paves the way to novel methods to engineer the emission of optical sources., The angular dependence is a well-known issue in metasurface engineering. Here the authors introduce a supercell metasurface able to implement multiple independent functions under large deflection angles with high efficiency, leading to a wavelength tunable laser with arbitrary wavefront control.

We demonstrate telecom-wavelength microcavities stabilized by dielectric metasurfaces. The approach achieves microcavities with quality factors exceeding 3300 using prevalent semiconductor manufacturing processes and opens the near-arbitrary field control of metasurfaces to cavity electrodynamics.

We present a mass-producible, all-glass, 100 mm diameter metalens working at visible wavelengths manufactured using deep-ultraviolet projection lithography, overcoming the intrinsic exposure size limit of the lithography tool.

We demonstrate stable optical microcavities by counteracting the phase evolution of the cavity modes using an amorphous silicon metasurface as one of the two cavity end mirrors. Careful design allows us to limit the metasurface scattering losses at telecom wavelengths to less than 2% and using a distributed Bragg reflector as metasurface substrate ensures high reflectivity. Our first demonstration experimentally achieves telecom-wavelength microcavities with quality factors of up to 4600, spectral resonance linewidths below 0.4 nm, and mode volumes down to below 2.7$\lambda ^3$. We then show that the method introduces unprecedented freedom to stabilize modes with arbitrary transverse intensity profiles and design cavity-enhanced hologram modes. Our approach introduces the nanoscopic light control capabilities of dielectric metasurfaces to cavity electrodynamics and is directly industrially scalable using widespread semiconductor manufacturing processes., Comment: 29 pages, 6 figures

Metasurfaces are a promising platform to exceed their traditional counterparts not only in compactness but also for functionality. However, current designs are limited when trying to implement multiple, non-paraxial functions with a single metasurface as they are bound to either a small angular range or to low efficiencies. Here, we present a new non-local metasurface design that enables the implementation of multiple, independent functions with a large difference in deflection angle. We further demonstrate the capabilities of this approach for advanced control of light emission systems by creating a wavelength-tunable external cavity laser with holographic output based on such metasurface.

The enigmatic interplay between electronic and magnetic phenomena observed in many early experiments and outlined in Maxwell’s equations propelled the development of modern electromagnetism1. Today, the fully controlled evolution of the electric field of ultrashort laser pulses enables the direct and ultrafast tuning of the electronic properties of matter, which is the cornerstone of light-wave electronics2–7. By contrast, owing to the lack of first-order interaction between light and spin, the magnetic properties of matter can only be affected indirectly and on much longer timescales, through a sequence of optical excitations and subsequent rearrangement of the spin structure8–16. Here we introduce the regime of ultrafast coherent magnetism and show how the magnetic properties of a ferromagnetic layer stack can be manipulated directly by the electric-field oscillations of light, reducing the magnetic response time to an external stimulus by two orders of magnitude. To track the unfolding dynamics in real time, we develop an attosecond time-resolved magnetic circular dichroism detection scheme, revealing optically induced spin and orbital momentum transfer in synchrony with light-field-driven coherent charge relocation17. In tandem with ab initio quantum dynamical modelling, we show how this mechanism enables the simultaneous control of electronic and magnetic properties that are essential for spintronic functionality. Our study unveils light-field coherent control of spin dynamics and macroscopic magnetic moments in the initial non-dissipative temporal regime and establishes optical frequencies as the speed limit of future coherent spintronic applications, spin transistors and data storage media. The magnetic properties of a ferromagnetic layer stack are controlled on attosecond timescales through optically induced spin and orbital momentum transfer, demonstrating a coherent regime of ultrafast magnetism.

The comb spacing of semiconductor comb lasers can be locked to an external reference by injecting a radio-frequency (RF) signal f inj close to the laser beat note round-trip frequency $f_{rt}^0$ [1] . This allows for controlling $f_{rt}^0$ and reducing its RF line width ∆ f rt . In this work, electrical-injection locking of a frequency-modulated quantum dash comb laser emitting at 1.57 µ m is demonstrated. Its round-trip frequency is $f_{rt}^0 = 20.1{\text{ GHz}}$ (cavity length 2 mm). The locking dynamics, recorded by direct detection of the comb’s output in the RF domain, are depicted in Fig. 1(a) for injection powers P inj from -10 dBm to 8 dBm. From -10 dBm up to 0 dBm, $f_{rt}^0$ and its -3 dB line width ∆ f rt remain unaffected. Within this range, the beat note line width amounts to 80 kHz. By increasing P inj from 0 dBm to 2.5 dBm, a pulling effect towards f inj becomes evident. For P inj > 2.5 dBm, the laser remains locked with ∆ f rt reduced to below 1 Hz, the microwave generator bandwidth. When sweeping f in j across $f_{rt}^0$ at P inj =8 dBm, Fig. 1(b) , two regimes evolve. For f inj outside the locking range of 1.8 MHz, $f_{rt}^0$ remains mostly unaffected with a small pulling effect for f inj close to the locking range. For frequencies inside the locking range ∆ f rt narrows to the bandwidth of the microwave oscillator and f rt follows f inj . Weak mixing side-band signals become apparent outside the locking range. Locking dynamics will be explained in more detail in the presentation. We employ the formalism of injection-locked coupled oscillators [2] and extend it by a noise term to take into account the stochastic origin of timing fluctuations. Results are depicted in Fig. 1(c) and Fig. 1(d) and are in agreement with the experiments. In order to quantify the improvement in phase noise of the comb by electrical injection locking $\left( {{f_{inj}} = f_{rt}^0} \right)$ , we measure phase noise spectra in dependence on P inj . Fig. 1(e) depicts increasing phase noise reduction by up to 20 dB at 100 kHz for increasing electrical injection strength. Simulation results ( Fig. 1(f) ) with a stochastic model [3] , developed for amplitude-modulated semiconductor comb lasers, are in excellent agreement with the experimental findings. Finally, we will show, that by joining both models, the comb laser beat note tuning can be directly linked with the phase noise reduction.

Transparent materials do not absorb light but have profound influence on the phase evolution of transmitted radiation. One consequence is chromatic dispersion, i.e., light of different frequencies travels at different velocities, causing ultrashort laser pulses to elongate in time while propagating. Here we experimentally demonstrate ultrathin nanostructured coatings that resolve this challenge: we tailor the dispersion of silicon nanopillar arrays such that they temporally reshape pulses upon transmission using slow light effects and act as ultrashort laser pulse compressors. The coatings induce anomalous group delay dispersion in the visible to near-infrared spectral region around 800 nm wavelength over an 80 nm bandwidth. We characterize the arrays’ performance in the spectral domain via white light interferometry and directly demonstrate the temporal compression of femtosecond laser pulses. Applying these coatings to conventional optics renders them ultrashort pulse compatible and suitable for a wide range of applications., Controlling the dispersion of femtosecond light pulses remains a key challenge for their application. Here, the authors report dispersion-engineered transmissive nanocoatings for ultrashort laser pulse compression in the vis-NIR spectral region.

The transition from frequency-modulated to amplitude-modulated frequency comb operation is studied experimentally in a multi-section InAs/InGaAs quantum dot frequency comb laser. Temporally and spectrally-resolved intensity and phase as well as time and frequency domain analysis allow to identify frequency-modulated and amplitude-modulated comb operation regimes in dependence on the laser gain current and absorber reverse bias voltage.

Optical self-injection stabilization of a passively mode-locked InGaAs double quantum well semiconductor laser is reported. Time-domain, frequency-domain and spectral domain measurement results in dependence on feedback strength and feedback delay demonstrate pulse width and higher harmonic mode-locking control. Traveling-wave equation simulations allow to explain the measured sequence of harmonic mode-locking orders in dependence on the feedback strength and delay.

We experimentally demonstrate a transmissive metasurface providing broadband negative group delay dispersion applicable in the visible to near-infrared region. The metacompressor can compress ultrashort laser pulses or compensate the dispersion of up to 4-mm-thick fused silica.

Metal–dielectric phase-shifting multilayer optical elements have been developed, providing broadband, virtually dispersion-free polarization manipulation down to the few-cycle level. These optical elements are A g / A l 2 O 3 mirrors that operate in the spectral range from 500 to 100 nm, exhibiting reflectance higher than 95%, and a differential phase shift between the s- and p-polarization of about 90° distributed over four bounces. The mirrors have been designed, produced, and reliably characterized based on spectral photometric and ellipsometric data using a non-parametric approach as well as a multi-oscillator model. The optical elements were implemented into a few-cycle laser system, where they transformed linearly polarized few-cycle light pulses to circular polarization.

With our experiment we demonstrate all-optical control of magnetization in a ferromagnet with an unprecedented sub-femtosecond time resolution. The reported results open the doors to a new generation of spintronic devices with petahertz clock-rates. (C) 2020 The Author(s)

We demonstrate a Petahertz bandwidth single-photon photoconductive switch by populating the conduction band in dielectrics with attosecond vacuum-ultraviolet (VUV) light pulses. Femtosecond pulse-driven currents reveal intra- and inter-band conduction band carrier dynamics.

We report measurements of the temporal dynamics of the valence band photoemission from the magnesium (0001) surface across the resonance of the Γ surface state at 134 eV and link them to observations of high-resolution synchrotron photoemission and numerical calculations of the time-dependent Schrödinger equation using an effective single-electron model potential. We observe a decrease in the time delay between photoemission from delocalized valence states and the localized core orbitals on resonance. Our approach to rigorously link excitation energy-resolved conventional steady-state photoemission with attosecond streaking spectroscopy reveals the connection between energy-space properties of bound electronic states and the temporal dynamics of the fundamental electronic excitations underlying the photoelectric effect., We thank F. Siegrist for experimental assistance, and we acknowledge financial support by the Munich Centre for Advanced Photonics (MAP). R. K. acknowledges an ERC Consolidator Grant “AEDMOS” (ERC-2014-CoG AEDMOS). D. P. acknowledges support from the “MEDEA” (H2020- MSCA-ITN-2014-641789-MEDEA).

Photodissociation of ozone following absorption of biologically harmful solar ultraviolet radiation is the key mechanism for the life protecting properties of the atmospheric ozone layer. Even though ozone photolysis is described successfully by post-Hartree-Fock theory, it has evaded direct experimental access so far, due to the unavailability of intense ultrashort deep ultraviolet radiation sources. The rapidity of ozone photolysis with predicted values of a few tens of femtoseconds renders both ultrashort pump and probe pulses indispensable to capture this manifestation of ultrafast chemistry. Here, we present the observation of femtosecond time-scale electronic and nuclear dynamics of ozone triggered by \ensuremath{\sim}10-fs, \ensuremath{\sim}2-\textmu{}J deep ultraviolet pulses and, in contrast to conventional attochemistry experiments, probed by extreme ultraviolet isolated pulses. An electronic wave packet is first created. We follow the splitting of the excited B-state related nuclear wave packet into a path leading to molecular fragmentation and an oscillating path, revolving around the Franck-Condon point with 22-fs wave-packet revival time. Full quantum-mechanical ab initio multiconfigurational time-dependent Hartree simulations support this interpretation.

Physical review / A covering atomic, molecular, and optical physics and quantum information 100(5), 053420 (2019). doi:10.1103/PhysRevA.100.053420, Highly brilliant, coherent, femtosecond x-ray pulses delivered by free-electron lasers (FELs) constitute oneof the pillars of modern ultrafast science. Next generation FEL facilities provide up to megahertz repetitionrates and pulse durations down to the attosecond regime utilizing self-amplification of spontaneous emission.However, the stochastic nature of this generation mechanism demands single-shot pulse characterization toperform meaningful experiments. Here we demonstrate a fast yet robust online analysis technique capableof megahertz-rate mapping of the temporal intensity structure and arrival time of x-ray FEL pulses withfew-femtosecond resolution. We performed angular streaking measurements of both neon photo- and Augerelectrons and show their applicability for a direct time-domain feedback system during ongoing experiments.The fidelity of the real-time pulse characterization algorithm is corroborated by resolving isolated x-ray pulsesand double pulse trains with few-femtosecond substructure, thus paving the way for x-ray-pump–x-ray-probeFEL science at repetition rates compatible with the demands of LCLS-II and European XFEL., Published by Inst., Woodbury, NY

The enigmatic interplay between electronic and magnetic phenomena observed in many early experiments and outlined in Maxwell's equations propelled the development of modern electromagnetism

We demonstrate the performance of a novel multilayer dielectric reflective thin-film attenuator capable of reshaping the super-octave spectrum of near-single-cycle visible laser pulses without deteriorating the phase properties of the reflected light. These novel broadband attenuating mirrors reshape in a virtually dispersion-free manner the incident spectrum such that the carrier wavelength of the reflected pulses shifts from ∼700 nm (Eγ=1.77 eV) to ∼540 nm (Eγ=2.25 eV) or beyond while maintaining their initial near-single-cycle pulse duration. This constitutes a viable approach to convert a number of established few-cycle ultrafast laser systems into sources with a selectable excitation wavelength to meet the requirements of single-color/multicolor high temporal resolution spectroscopic experiments.

Attosecond photoelectron streaking spectroscopy allows time-resolved electron dynamics with a temporal resolution approaching the atomic unit of time. Studies have been performed in numerous systems, including atoms, molecules, and surfaces, and the quest for ever higher temporal resolution called for ever wider spectral extent of the attosecond pulses. For typical experiments relying on attosecond pulses with a duration of 200 as, the time-bandwidth limitation for a Gaussian pulse implies a minimal spectral bandwidth larger than 9 eV translating to a corresponding spread of the detected photoelectron kinetic energies. Here, by utilizing a specially tailored narrowband reflective XUV multilayer mirror, we explore experimentally the minimal spectral width compatible with attosecond time-resolved photoelectron spectroscopy while obtaining the highest possible spectral resolution. The validity of the concept is proven by recording attosecond electron streaking traces from the direct semiconductor gallium arsenide (GaAs), with a nominal bandgap of 1.42 eV at room temperature, proving the potential of the approach for tracking charge dynamics also in these technologically highly relevant materials that previously have been inaccessible to attosecond science.

Recent advances in the development of attosecond soft x-ray sources toward photon wavelengths below 10 nm are also driving the development of suited broadband multilayer optics for steering and shaping attosecond pulses. We demonstrate that current attosecond experiments in the sub-200-eV range benefit from these improved optics. We present our achievements in utilizing ion-beam-deposited chromium/scandium (Cr/Sc) multilayer mirrors, optimized by tailored material dependent deposition and interface polishing, for the generation of single attosecond pulses from a high-harmonic cut-off spectrum at a central energy of 145 eV. Isolated attosecond pulses have been measured by soft x-ray-pump/NIR-probe electron streaking experiments and characterized using frequency-resolved optical gating for complete reconstruction of attosecond bursts (FROG/CRAB). The results demonstrate that Cr/Sc multilayer mirrors can be used as efficient attosecond optics for reflecting 600-attosecond pulses at a photon energy of 145 eV, which is a prerequisite for present and future attosecond experiments in this energy range.

A multitude of physical effects have been proposed to determine the photoemission delay between core and valence electrons in tungsten. We present selected streaking experiments that clarify its origins.

We present an optical investigation of surface plasmon polaritons propagating along nanoscale Au-wires, lithographically defined on GaAs substrates. A two-axis confocal microscope was used to perform spatially and polarization resolved measurements in order to confirm the guiding of surface plasmon polaritons over lengths ranging from $5-20 \mu m$ along nanowires with a lateral dimension of only $\approx 100 nm$. Finite difference time domain simulations are used to corroborate our experimental observations and highlight the potential to couple proximal quantum dot emitters to propagating plasmon modes in such extreme sub-wavelength devices. Our findings are of strong relevance for the development of semiconductor based integrated plasmonic and active quantum plasmonic nanosystems that merge quantum emitters with nanoscale plasmonic elements., Comment: 6 pages, 4 figures

We introduce a viable scheme for measuring the absolute duration of photoemission from solids. It employs an atomic chronograph on the surface during attosecond streaking spectroscopy. First experimental results on a tungsten(110) surface are presented.

The development of new high power laser sources tends toward optical parametric chirped pulse amplification (OPCPA) in recent years. One of the difficulties in OPCPA is the the temporal overlap between pump and seed pulses. In this work we characterize our timing jitter on a single-shot basis using spectrally resolved cross-correlation in combination with a position sensitive detector. A commercial beam stabilization is adapted to actively enhance temporal overlap. This delay-stabilizer reduces the RMS jitter from σ = 127 fs down to σ = 24 fs. The enhanced temporal overlap is demonstrated in our frontend and we propose the scheme to be applicable in many optically synchronized high-repetition-rate OPCPA systems.

We produce carrier-envelope-phase-stable 10.5 fs (1.5-optical-cycle) 1.2mJ pulses at 2.1-μm carrier wavelength by a three-stage optical parametric chirped-pulse amplifier system. Furthermore, we have generated atomic high-harmonics beyond 1 keV photon energy with this unique source.

We produce 1.5 cycle (10.5 fs), 1.2 mJ, 3 kHz carrier-envelope-phase-stable pulses at 2.1 μm carrier wavelength, from a three-stage optical parametric chirped-pulse amplifier system, pumped by an optically synchronized 1.6 ps Yb:YAG thin disk laser. A chirped periodically poled lithium niobate crystal is used to generate the ultrabroad spectrum needed for a 1.5 cycle pulse through difference frequency mixing of spectrally broadened pulse from a Ti:sapphire amplifier. It will be an ideal tool for producing isolated attosecond pulses with high photon energies.

Photoemission of an electron is commonly treated as a one-particle phenomenon. With attosecond streaking spectroscopy we observe the breakdown of this single active-electron approximation by recording up to six attoseconds retardation of the dislodged photoelectron due to electronic correlations. We recorded the photon-energy-dependent emission timing of electrons, released from the helium ground state by an extreme-ultraviolet photon, either leaving the ion in its ground state or exciting it into a shake-up state. We identify an optical field-driven d.c. Stark shift of charge-asymmetric ionic states formed after the entangled photoemission as a key contribution to the observed correlation time shift. These findings enable a complete wavepacket reconstruction and are universal for all polarized initial and final states. Sub-attosecond agreement with quantum mechanical ab initio modelling allows us to determine the absolute zero of time in the photoelectric effect to a precision better than 1/25th of the atomic unit of time. Photoemission is not a simple process and it is not instantaneous. Delays of a few attoseconds have now been measured in helium and it seems that they are partly due to electronic correlations.

Photoemission spectroscopy is central to understanding the inner workings of condensed matter, from simple metals and semiconductors to complex materials such as Mott insulators and superconductors1. Most state-of-the-art knowledge about such solids stems from spectroscopic investigations, and use of subfemtosecond light pulses can provide a time-domain perspective. For example, attosecond (10-18 seconds) metrology allows electron wave packet creation, transport and scattering to be followed on atomic length scales and on attosecond timescales2-7. However, previous studies could not disclose the duration of these processes, because the arrival time of the photons was not known with attosecond precision. Here we show that this main source of ambiguity can be overcome by introducing the atomic chronoscope method, which references all measured timings to the moment of light-pulse arrival and therefore provides absolute timing of the processes under scrutiny. Our proof-of-principle experiment reveals that photoemission from the tungsten conduction band can proceed faster than previously anticipated. By contrast, the duration of electron emanation from core states is correctly described by semiclassical modelling. These findings highlight the necessity of treating the origin, initial excitation and transport of electrons in advanced modelling of the attosecond response of solids, and our absolute data provide a benchmark. Starting from a robustly characterized surface, we then extend attosecond spectroscopy towards isolating the emission properties of atomic adsorbates on surfaces and demonstrate that these act as photoemitters with instantaneous response. We also find that the tungsten core-electron timing remains unchanged by the adsorption of less than one monolayer of dielectric atoms, providing a starting point for the exploration of excitation and charge migration in technologically and biologically relevant adsorbate systems.

We determined the photoemission timing of electrons escaping during shake-down and shake-up processes in helium with sub-attosecond standard error. Excellent agreement with ab-initio calculations allows benchmarking of theoretical models and identifies contributions of electronic correlation.